Question

[Cao Như Ngọc]

Bài 2: Tính nhanh

a) 27 + ( -2019 ) + ( -27 )

b) ( -10 ) + 23 + ( -20 ) + 30

c) ( -2 ).125.( -5 ).( -8 ).( +17 )

d) ( -9 ) + ( -15 ) + ( -33 )

e) ( -15 ).6

f) 5.( -9 ) + 4.9

Answer 1

[santa]

a) 27 + ( -2019 ) + ( -27 )

= [ 27 + ( - 27) ] + ( - 2019)

= 0 - 2019

= - 2019

b) ( -10 ) + 23 + ( -20 ) + 30

= [ ( - 10 ) + (- 20) + 30]+ 23

= [ ( - 30) + 30] + 23

= 0 + 23 = 23

c) ( -2 ).125.( -5 ).( -8 ).( +17 )

= [ - 2 . ( - 5 )] . [ 125 . ( - 8)] . 17

= 10 . 1000 . 17

= 170000

d) ( -9 ) + ( -15 ) + ( -33 )

= - 24 + ( - 33 )

= - 57

e) ( -15 ).6 = - 80

f) 5.( -9 ) + 4.9 = 9 . ( - 5 + 4) = 9 . 1 = 9